1. Field of the Invention
The present invention relates to a combustor for a gas turbine that can prevent oil in a manifold from coking.
2. Description of the Related Art
The combustor for the gas turbine has a plurality of main nozzles around a pilot nozzle. A plurality of such combustors are disposed around a casing of the gas turbine. A dual-type combustor is a combustor that switches fuels from oil-fired to gas-fired. In the dual-type combustor, the pilot nozzle thereof is dually structured including a central pipe through which pilot oil-fuel flows and an outer pipe, which is provided around the central pipe, where pilot gas-fuel flows. The main nozzle is also dually structured including a central pipe for the oil-fuel and an outer pipe for the gas-fuel.
FIG. 6 is a front view of the nozzle of the combustor, and FIG. 7 is an explanatory schematic of the oil-fuel supply lines. As shown in FIG. 6, the pilot nozzle 1 is allocated in the center of the combustor 500, and eight main nozzles 2 are aligned around the pilot nozzle 1, both the pilot nozzle and main nozzles can combust the oil-fuel and the gas-fuel by switching the fuels. Among the main nozzles 2, the nozzles with hatching are main-A-nozzles 2a, the nozzles without the hatching are main-B-nozzles 2b, and 2a and 2b are alternately disposed. As shown in FIG. 2, the combustor 500 is provided with three fuel lines, which are a main-A line 501, a main-B line 502, and a pilot line 503. The fuel is supplied to each line separately.
The main-A-nozzles 2a and the main-B-nozzles 2b have an oil-fuel supply port each. However, in a midway, 2a and 2b respectively have a manifold 510 and 511, which distribute the oil-fuel to each main nozzle 2. To be more specific, as shown in FIG. 8, 2a and 2b constitute a nozzle pipe stand 515 by laying disk shaped members 512, 513, and 514. Each disk shaped member 512 to 514 forms a hole 516 in a center thereof, through which the pilot nozzle passes, and have grooves 519 and 520 formed with ring shaped protruding portions 517 and 518, which constitute the manifolds 510 and 511. The grooves 519 and 520 respectively have four holes bored through which center pipes of the main nozzles 2 pass. The disk shaped members 512 and 513, which cover the grooves 519 and 520, are provided with pipes 522 and 523 that communicatively connect an oil-fuel supply unit with the grooves 519 and 520. The disk shaped members 512 to 514 are welded and fixed in a state the disk shaped members 512 and 513 are being laid and assembled together.
In the structure mentioned above, the main-A line 501 and main-B line 502 come to possess branches in the nozzle pipe stand 515 as shown in FIG. 7. It is possible to emit the fuel from the eight main nozzles 2 ((1) to (8) in FIG. 7) by supplying the oil-fuel from a pipe A and pipe B. Emitted fuel mixes with compressed air that is sent from a compressor and burns.
A little amount of oil remains in the manifolds 510 and 511 after the gas turbine is stopped, or in the case of the dual-type combustor, after being switched from the oil-fuel to the gas-fuel. It is usually the case to discharge the remaining oil from the manifolds by taking in purging air from the pipe A and pipe B. However, as shown in FIG. 9, oil 40 remains in a lower part of the manifolds because the manifolds 510 and 511 are circular in shape. Meanwhile, temperatures of the main nozzles 2 rise, because the nozzles receive heat from the casing after the gas turbine is stopped or while the gas turbine is being operated by the oil-fuel. The remaining oil in the manifolds 510 and 511 of the nozzles 2 is heated and causes coking that results in a problem by blocking the nozzles due to a phenomenon mentioned above.
Therefore, it is an object of the present invention to provide a combustor that can prevent coking from occurring, which will otherwise occur in the manifolds that branch pipes for the oil-fuel provided to the nozzle pipe stand.